The present invention generally relates to a biosensor, and more particularly to a biosensor including a sensing gate dielectric and a back gate dielectric
Biosensors may have a variety of applications. For example, a biosensor may be used in DNA sequencing or virus screening. Additionally, biosensors may be employed to detect a biocharge in DNA, protein, and cancer cells. As an example, detection of a biocharge may be correlated with an amount of DNA present in a chamber. Thus, a biosensor employing biocharge detection may be used to quantitatively determine an amount of DNA that is present in a test chamber.
One type of biosensor is ion-sensitive field-effect transistor (ISFET). An ion-sensitive field-effect transistor (ISFET) may be used for measuring ion concentrations in solution. For example, when the ion concentration (such as H+) changes, the current through a transistor may change accordingly. Thus, the solution may be used as the gate electrode. When a biospecies (e.g., DNA) lands on the gate dielectric of an ISFET, the charges carried by the biospecies may modulate the electrical current in the channel of the ISFET. Sensing may be achieved by monitoring a change of the transistor characteristics (e.g., threshold voltage (Vt)).
However, relatively small amounts of a biospecies, such as DNA, may carry a relatively small amount of charge. Thus, a Vt shift may be relatively small when the DNA sample is placed in the test chamber.